This invention relates to a controlled microorganism degradation process for decontaminating soil or sediments contaminated with one or more PCB
Polychlorinated biphenyls (PCBs) have been produced as complex mixtures for a variety of uses, including dielectric fluids in capacitors and ransformers. Arochlor PCBs (Monsanto Corporation) were marketed for use in transfrmeers, capacitors, printing inks,. Paints, de-dusting agents, pesticides and many other uses. PCBs in general are mixtures of several compounds, called congeners, in which one to ten chlorine atoms are attached to biphenyl. They are often described by the wt. % chlorine contained, e.g. Archlor 1221, 1242 and 12260 contain 21, 42, and 60 wt. % chlorine.
Numerous land sites exist that are contaminated, and have been contaminated for decades, with the highly toxic PCBs. Many of these sites are unusable and will remain unusable until some economical process becomes available for large scale decontamination of the soil of such sites.
Zeneca Corp. U.S. Pat. Nos. 5,660,612 and 5,660,613 disclose the remediation of soil contaminated with the non-aromatic pesticide DDT by anaerobic composting followed aerobic composting under specific conditions of water content, temperature, redox potential and the presence of unacclimated soil--indigenous anaerobic and aerobic microbes capable of transforming DDT into harmless materials.
We have tried this method in attempts to decontaminate soil containing various contaminants other than DDT. While this method has been found successful with a limited number of specific contaminants, it was unsuccessful for many contaminants. There appears to be no reliable way to predict which compounds will be effectively decomposed by this method, and particularly no reason to expect that it would be successful, as with DDT, in decontaminating soil containing the chemically different aromatic PCBs.
Several researchers have attempted to degrade PCBs by complex composting in aqueous slurries under a sequence of anaerobic and aerobic treatments requiring the addition of separate inoculants before each anaerobic and aerobic treatment, and the addition of byphenyl to enhance the degradation. PCB decomposition was achieved over an excessively long time. See "Sequential Anaerobic-Aerobic Biodegradation of PCBs in Soil Slurry Microcosms", B. S. Evans, C. A. Dudley and K. T. Klasson, 1996, Applied Biochemistry and Biotechnology, Vol. 57/58, 885-894.
The present invention does not require two stages of composting treatment, two separate microbe inoculants, or a slurry environment.